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| #38481 (Received by flhurricane at: 4:34 AM 09.Aug.2005) TCDAT4 TROPICAL DEPRESSION IRENE DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT TUE AUG 09 2005 THERE HAS BEEN SOME INCREASE IN THE DEEP CONVECTION NEAR THE CENTER OF IRENE'S MOSTLY EXPOSED CIRCULATION. WHILE THERE MAY WELL BE 35 KT WINDS IN THE SYSTEM AT THIS MOMENT...I WOULD PREFER TO SEE THIS CONVECTION PERSIST NEAR THE CENTER BEFORE RE-UPGRADING IRENE TO A TROPICAL STORM. THE 6Z DVORAK INTENSITY ESTIMATES WERE 25-30 KT...AND THE INITIAL INTENSITY WILL BE HELD AT 30 KT FOR THIS ADVISORY. IRENE IS PRESENTLY MOVING PAST A BREAK IN THE MID-LEVEL SUBTROPICAL RIDGE...WITH THE RIDGE CURRENTLY WELL ESTABLISHED AT MID- TO UPPER LEVELS TO THE NORTHWEST OF THE CYCLONE. THIS PATTERN IS IMPARTING A NORTHERLY FLOW OF VERY DRY AIR AT UPPER LEVELS OVER IRENE THAT IS HINDERING DEVELOPMENT. GLOBAL MODELS INDICATE THAT THIS UPPER FLOW SHOULD TRANSITION TO SOUTHEASTERLIES OVER THE NEXT COUPLE OF DAYS AS IRENE MOVES CLOSER TO...AND TO THE NORTHEAST OF THE UPPER LOW CURRENTLY NEAR 30N/73W. SOME RESTRENGTHENING IS THEREFORE SHOWN IN THE OFFICIAL FORECAST. HOWEVER...THIS STRENGTHENING IS CONSIDERABLY LESS THAN INDICATED BY THE SHIPS GUIDANCE...WHICH BRINGS IRENE TO NEARLY HURRICANE STRENGTH IN FIVE DAYS. AN OPPOSING VIEW IS PROVIDED BY THE GFDL MODEL...WHICH DISSIPATES IRENE WITHIN 24 HOURS. AS IRENE HAS PERSERVERED THROUGH AN ENVIRONMENT SEEMINGLY MORE HOSTILE THAN WHAT IT IS CURRENTLY EMBEDDED IN...I AM GETTING LESS HOPEFUL ABOUT THE DISSIPATION OPTION. THE INITIAL MOTION IS 270/10. THE MID-LEVEL SUBTROPICAL RIDGE...CURRENTLY CENTERED NEAR BERMUDA...IS FORECAST BY THE GFS...UKMET...NOGAPS...AND CANADIAN MODELS TO MOVE SOUTHWESTWARD AND/OR SPLIT AND WEAKEN OVER THE NEXT THREE DAYS. ALL OF THESE MODELS SHOW A SHORT WAVE TROUGH IN THE WESTERLIES MOVING INTO THE WESTERN ATLANTIC IN ABOUT THREE DAYS...AND THESE MODELS ALL LIFT IRENE...OR ITS REMNANTS...NORTHWESTWARD WITH THE APPROACH OF THIS TROUGH. THE 00Z RUNS OF THE UKMET AND NOGAPS MODELS...HOWEVER... LEAVE IRENE TO LINGER BEHIND AS THE TROUGH PROGRESSES EASTWARD. THERE IS ALSO A CURIOUS SEPARATION BETWEEN THE SINGLE-LAYER BAM MODELS AND THE MULTI-LEVEL GLOBAL MODELS...WITH THE BAM MODELS ALL SHOWING A MORE STRAIGHT-LINE WEST-NORTHWESTERLY TRACK THROUGH THE FIVE DAY PERIOD. AMONG THE BAM MODELS...THE SHALLOW BAM HAS THE MOST NORTHERLY TRACK...WHICH IS CONSISTENT WITH THE NORTHERLY UPPER-LEVEL FLOW CURRENTLY OVER THE TROPICAL CYCLONE. THE OFFICIAL FORECAST HAS BEEN SHIFTED JUST A LITTLE TO THE WEST OF THE PREVIOUS ADVISORY AND IS ALSO SLOWER AT DAYS 4 AND 5. THE OFFICIAL FORECAST LIES CLOSE TO THE LEFT EDGE OF THE GLOBAL MODEL GUIDANCE ENVELOPE...AND IS ALSO CLOSE TO THE SHALLOW BAM FOR THE FIRST 72 HOURS. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 09/0900Z 22.5N 53.6W 30 KT 12HR VT 09/1800Z 22.5N 55.2W 30 KT 24HR VT 10/0600Z 23.0N 57.4W 35 KT 36HR VT 10/1800Z 23.9N 59.4W 35 KT 48HR VT 11/0600Z 25.2N 61.4W 40 KT 72HR VT 12/0600Z 27.5N 64.5W 40 KT 96HR VT 13/0600Z 29.0N 65.5W 45 KT 120HR VT 14/0600Z 30.0N 66.0W 45 KT |
